Uncooled microbolometer arrays are extremely sensitive to changes in FPA substrate temperature. For example, in a typical microbolometer IR camera, a change in the substrate temperature of 0.0025° C. corresponds to about a 0.1° C. apparent change in the scene temperature. Accordingly, significant design effort goes into calibrating out the average change in substrate temperature that can occur during normal operation, due either to device self-heating or to changes in the environment. Compensation for the average change in substrate temperature may be achieved through bias and/or offset correction circuitry implemented in the FPA, and/or through a software algorithm that compensates each pixel's output as a function of FPA temperature as detected by a precision temperature sensor onboard the FPA. However, in many cases, heating of the FPA substrate is not uniform. This non-uniformity in heating cannot be compensated for by a single temperature sensor, with the result that additional fixed pattern noise can occur in the image. Additionally, the traditional method of using a shutter to compensate for fixed pattern noise is not available in some devices. While some scene-based non-uniformity compensation (SBNUC) techniques do a satisfactory job of removing high spatial frequency non-uniformity, they do not work well in cases of low spatial frequency non-uniformity, as might well be encountered if the FPA substrate temperature gradient changes.
Accordingly, a need exists for mechanisms that can reduce thermal gradients in IR FPAs which cause image non-uniformity and result in non-scene related changes in device output levels.